The purpose of this informal workshop is to discuss and exchange ideas on recent developments at the interface of modern cosmology and fundamental physics. This workshop is the seventh in a series organized jointly by the International Solvay Institutes, APC (Université Paris VII, Paris) and the Perimeter Institute (Waterloo, Canada). The previous edition was held in Brussels in May, 2012.

James Bardeen, University of Washington Black hole evaporation and unitarity: a semi-classical resolution? I explore the possibility that semi-classical back-reaction, due to the partners of the Hawking radiation quanta accumulating over the time for the black hole to lose about one half of its mass (the Page time), might cause the trapped surfaces to disappear, permitting unitary evolution without any cloning of quantum information. Richard Bond, University of Toronto Intermittent non-Gaussianity & Anomalies: rare patchy subdominants from Modulated Heating, Bubble Collisions & OscillonsMartin Bucher, Laboratoire de Physique Theorique d'Orsay Planck and beyondAfter reviewing some of the highlights of the implications of the Planck results for cosmic inflation (presentation to be coordinated with Hiranya Peiris), I will discuss some recent developments regarding future searches for B modes and other new science resulting from an ultra-precise characterization of the microwave and far-infrared sky in polarization. I will outline ideas for a recently proposed large-class European Space Agency mission called PRISM.Ben Craps, VUB & Solvay InstitutesStrings in Compact Cosmological SpacesA formalism is proposed for perturbative string theory in spacetimes with totally compact space (and non-compact time).Neal Dalal, University of Illinois at Urbana-Champaign Probing small-scale structure with dusty galaxies in the CMBDaniel Green, Stanford UniversityHow much information is there in large scale structure?Large scale structure contains vastly more Fourier modes than the CMB, and is therefore a promising arena for studying the early universe. One obstacle to using these modes is the non-linearity of structure formation. The amount of weakly coupled information available is therefore very sensitive to scale at which non-linear effects become important and simulations become necessary. Using effective field theory techniques, I will present evidence that the perturbative description of dark matter is much better behaved than previously thought. I will discuss the implications for improving constraints on non-gaussian initial conditions.Fawad Hassan, Stockholm University Bimetric theory, Conformal Gravity and Partial Masslessness Ghost-free bimetric theories can be used to describe gravitational interactions in the presence of an extra neutral massive spin-2 field that can modify gravity in non-trivial ways. They also provide a natural framework for a possible non-linear extension of partially masslessness known to arise in linear Fierz-Pauli theory. This talk will describe bimetric theories and a procedure that identifies a unique bimetric action as a candidate for a nonlinear partially massless theory. We then show that in the low curvature limit, the candidate partial massless theory is related to Conformal Gravity. Marc Henneaux, Solvay InstituteRemarks on Gravitational DualityKurt Hinterbichler, Perimeter Institute Cosmological Consistency Relations as Ward IdentitiesRenee Hlozek, Princeton UnviersityThe Microwave Background on small scales: Cosmological parameters from three seasons of data of the Atacama Cosmology Telescope (ACT).

The Atacama Cosmology Telescope (ACT) has mapped the microwave sky to

arcminute scales. We present constraints on parameters from the observations at 148 and 217 GHz respectively by ACT from three years of observations. Efficient map-making and spectrum-estimation techniques allow us to probe the acoustic peaks deep into the damping tail, and allow for confirmation of the concordance model, and tests for deviations from the standard cosmological picture. We fit a model of primary cosmological and secondary foreground parameters to the dataset, including contributions from both the thermal and kinetic Sunyaev-Zel'dovich effect, Poisson distributed and correlated infrared sources, radio sources and a term modeling the correlation between the thermal SZ effect and the Cosmic Infrared Background. We will describe the multi-frequency likelihood for the ACT data, and present constraints on a variety of cosmological parameters using this

complete dataset, and put these results in context with the recent results from the Planck satellite.

David Langlois, APC Paris

A unifying approach to dark energy models

This talk will present an effective description of single field dark energy/modified gravity models, which encompasses most existing proposals. The starting point is a generic Lagrangian expressed in terms of the lapse and of the extrinsic and intrinsic curvature tensors of the uniform scalar field hypersurfaces. By expanding this Lagrangian up to quadratic order, one can describe the homogeneous background and the dynamics of linear perturbations. In particular, one can identify seven Lagrangian operators that lead to equations of motion containing at most second order derivatives, the time-dependent coefficients of three of these operators characterizing the background evolution. I will illustrate this approach with Horndeski's---or generalized Galileon---theories. Finally, I will discuss the link between this effective approach and observations.

Paul McFadden, Perimeter Institute

Precision Holographic Cosmology

We discuss holography for cosmology, focusing on a class of slow-roll inflationary spacetimes that are holographically dual to a perturbative RG flow between two nearby CFTs. The cosmological power spectrum and non-Gaussianities may be calculated directly from the dual QFT using conformal perturbation theory, even when the dual QFT is strongly coupled. Holography thus offers new methods for computing cosmological observables. To illustrate, we show how to recover the power spectrum to second order in slow roll.

Pulsar timing arrays (PTAs), which are currently operating around the world and achieving remarkable sensitivities in the ~1--‐100 nHz band, will observe supermassive black holes (SMBHs) at redshifts z < ~1. Until now, all estimates of the anticipated signal strength of these sources have relied primarily on simulations to predict the relevant merger rates. I will present results from a completely new approach, which combines observational data and a fully self--‐consistent numerical evolution of the galaxy mass function. This method, which we will argue is superior to past estimates in several key ways, predicts a merger rate for massive galaxies that is ~10 times larger than that implied by previous calculations. I will explain why previous methods applied to this problem may systematically underestimate this merger rate, and one way in which our method may overestimate the rate, so that our approach has complementary systematic uncertainties in the worst case, and is an overall improvement in the best case. Finally, I will show that the new rate implies a range of possible signal strengths that is already in mild tension with PTA observations, with our model predicting a detection at the 95% confidence level as early as 2016. This could make PTAs the first instruments to directly detect gravitational waves, and will provide unprecedented information about the dynamics of merging galaxies, and merging bulges and supermassive black holes within those galaxies.

Shinji Mukohyama, Kavli IPMU

Massive gravity and cosmology

Alberto Nicolis, Columbia University

Solid Inflation

I will describe a cosmological model where primordial inflation is driven by a 'solid', defined as a system of three derivatively coupled scalar fields obeying certain symmetries and spontaneously breaking a certain subgroup of these. The symmetry breaking pattern differs drastically from that of standard inflationary models: time translations are unbroken. This prevents our model from fitting into the standard effective field theory description of adiabatic perturbations, with crucial consequences for the dynamics of cosmological perturbations. Most notably, non-gaussianities in the curvature perturbations are unusually large, with f_NL ~ 1/(\epsilon.c_s^2), and have a novel shape: peaked in the squeezed limit, with anisotropic dependence on how the limit is approached. Other unusual features include the absence of adiabatic fluctuation modes during inflation---which does not impair their presence and near scale-invariance after inflation---and a slightly blue tilt for the tensor modes.

Hiranya Peiris, London's Global University

Testing inflation with combined power- and bispectrum

Ue-LiPen, CITA

21cm cosmology

I will overview the progress of 21cm cosmology, with emphasis on intensity mapping. Current and future experiments have the potential for precision measurements of dark energy, neutrino mass, and gravitational waves.

Suvrat Raju, International Centre for Theoretical Sciences

The Information Paradox and an an Infalling Observer in AdS/CFTKris Sigurdson, University of British ColumbiaCosmological Limits on Neutrino-Neutrino Scattering and Particle Physics in the Early UniverseIn the standard model neutrinos are assumed to have streamed across the Universe since they last scattered at the weak decoupling epoch when the temperature of the standard-model plasma was ~MeV. The shear stress of free-streaming neutrinos imprints itself gravitationally on the Cosmic Microwave Background (CMB) and makes the CMB a sensitive probe of neutrino scattering. Yet, the presence of nonstandard physics in the neutrino sector may alter this standard chronology and delay neutrino free-streaming until a much later epoch. We will discuss how observations of the CMB can be used to constrain the strength of neutrino self-interactions G_eff and put limits on new physics in the neutrino sector from the early Universe. Key measurements of the CMB at large multipoles made by the Planck satellite and high-l experiments are critical for probing this physics. Within the context of conventional LambdaCDM parameters cosmological data are compatible with G_eff < 1/(56 MeV)^2 and neutrino free-streaming might be delayed until their temperature has cooled to as low as ~25 eV. Intriguingly, we also find an alternative cosmology compatible with cosmological data in which neutrinos scatter off each other until z~10^4 with a preferred interaction strength in a narrow region around G_eff = 1/(10 MeV)^2. This distinct self-interacting neutrino cosmology is characterized by somewhat lower values of both the scalar spectral index and the amplitude of primordial fluctuations. We phrase our discussion in terms of a specific scenario in which a late onset of neutrino free-streaming could occur, but in fact our constraints on the neutrino visibility function are very general. Kendrick Smith, Perimeter Institute & Princeton University

Primordial non-Gaussianity in the CMB and large-scale structure

Neil Turok, Perimeter Institute

Resolution of Cosmic Singularities and Bounces

The AdS/CFT correspondence provides new insights and tools to answer previously inaccessible questions in quantum gravity. Among the most interesting is whether it is possible to describe a cosmological "bounce" in a mathematically complete and consistent way. In the talk, I'll discuss joint work with M. Smolkin, developing the dual description of the simplest possible 4d M-theory cosmology in the stringy regime, employing the full quantum dynamics of its dual CFT. I'll also present evidence that the description extends to the Einstein-gravity regime.

Large scale structure contains vastly more Fourier modes than the CMB, and is therefore a promising arena for studying the early universe. One obstacle to using these modes is the non-linearity of structure formation.

Pulsar timing arrays (PTAs), which are currently operating around the world and achieving remarkable sensitivities in the ~1--‐100 nHz band, will observe supermassive black holes (SMBHs) at redshifts z

The Atacama Cosmology Telescope (ACT) has mapped the microwave sky toarcminute scales. We present constraints on parameters from the observations at 148 and 217 GHz respectively by ACT from three yearsof observations. Efficient map-making and spectrum-estimation techniques allow us to probe the acoustic peaks deep into the damping tail, and allow forconfirmation of the concordance model, and tests for deviations fromthe standard cosmological picture. We fit a model of primarycosmological and secondary foreground parameters to the dataset,

I explore the possibility that semi-classical back-reaction, due to the partners of the Hawking radiation quanta accumulating over the time for the black hole to lose about one half of its mass (the Page time), might cause the trapped surfaces to disappear, permitting unitary evolution without any cloning of quantum information.